This invention relates to an apparatus for live harvesting of an aquatic target species at depth and bringing it to a collection point at the surface of a waterbody in a manner which substantially reduces the mortality rate. In addition, this apparatus permits ready separation, either or both at the surface collection point, or during transportation to the surface collection point, of live target and any non-target species harvested simultaneously from the waterbody and facilitates the reintroduction of the non-target species at depth to the waterbody.
Conventional practice for the mass harvesting of relatively small aquatic target species such as shrimp is usually accomplished by using trawl nets, or the like, which are towed behind a trawler. These nets catch both the target and non-targeted or by-catch species indiscriminately. As the volume of bio-mass is compressed into the collection end, or cod end, of the trawl net as it is moved through the water body, a high mortality of both target and by-catch species results. In addition, this compression and the subsequent lifting movement of the filled net from depth to the surface of the water body and its transportation onboard the trawl boat results in additional mortality and inflicts damage to the target species resulting in a decrease in quality.
Public pressure and regulation now require that more attention to be paid to limiting the mortality rate of the by-catch, since much of it is made up of juveniles of commercially valuable species. The mortality of such juvenile by-catch species is the result of compaction and suffocation in the cod-end of the trawl net during netting, and as the net is hauled onboard the trawler and the inability to survive the temperature differential of the water from the point of catch to the point of release at the surface of the water body.
Without intending to be limiting, it is an object of this invention to transport both target and by-catch species live to a container at the surface of a water body along with a constant volume of water from the depth at which the species were caught.
Again without intending to be limiting, it is a further object of this invention to provide a means of escapement for by-catch species during the transportation of by-catch and target species to the surface.
Again without intending to be limiting, it is a further object of this invention to provide a means of separating target and by-catch within the surface container and returning the by-catch directly to depth to thereby reduce mortality.
Further, this invention overcomes inherent difficulties where the target species and by-catch species are quite similar in size and where the by-catch species is an endangered species.
Applicant is aware that many bodies of fresh water have in the past seen the introduction of nonindigenous aquatic organisms intended as an additional forage source for indigenous sport fish. In some cases the introduced species has resulted in dramatically adverse changes to the aquatic ecosystem and has become a direct competitor for available food resources, placing the indigenous species in even greater peril. Such has been the experience with the introduction of Mysis relicta, a.k.a. Opossum shrimp or Mysis shrimp as a food source for Oncorhynchus nerka kennerlyi a.k.a. Kokanee, land-locked sockeye or silver trout. Control of the Mysis shrimp population through an aggressive harvesting program is therefore seen as a major component of a plan to protect what has become, in some lakes, an endangered species, namely the Kokanee.
In the prior art Applicant is aware of U.S. Pat. No. 3,768,193, which issued Oct. 30, 1973 to London for a Brine Shrimp Harvesting Apparatus. London discloses a method of using a elongated housing containing a rotatable internal screw, mounted on a raft, for removing shrimp concentrated on a net at the surface of a water body. Applicant is further aware of U.S. Pat. No. 5,361,528 which issued Nov. 8, 1994 to Peacock for a Trawling System and Trawl Device for Shrimp. Peacock discloses a device having angularly adjustable opposed elongated arms for trawling over the seabed. Water pressure as the trawl is moved over the seabed forces shrimp to the outer extremities of the elongated arms where they can be drawn to the trawl boat by onboard pumps.
What is neither taught nor rendered obvious from the prior art, and which is an object of the present invention to provide is an apparatus which permits ready separation, at the surface collection point, of live target and any non-target species harvested simultaneously from a body of fresh water and which facilitates the reintroduction of the non-target species to the waterbody at a depth where the water temperature is generally the same as where they were harvested thereby reducing mortality of the non-target species.
The present invention relates to a device for harvesting a target species, which in this example is, but not limited to, a variety of fresh water shrimp, separating from the target species any non-target species, such as juveniles of a commercially valuable sport fishery species such as Kokanee salmon which have been inadvertently and simultaneously harvested and releasing the non-target species back to the same depth and water temperature at which they were caught.
The device of the present invention includes a trawl net and a catch boat each being towable by a trawler by separate towing lines or cables so as to be movable concomitantly through the water by the trawler. A catch drawer is mounted within the catch boat for selective vertical movement relative thereto by a means for selective vertical movement of the catch drawer in relation to the catch boat. A conduit connects the cod-end of the trawl net to a forward end of the catch drawer. The conduit permits both target and by-catch species to be freely carried through the conduit along with a constant volume of water, which is funneled through the conduit as the trawl net is pulled through the water.
A pump or other means maintains the surface level of water in the catch drawer below the surface level of the lake or other large body of water in which the device of the present invention is situate.
A series of removable nets or screens are positioned within the catch drawer for separating target and by-catch species. A means is provided to convey by-catch organisms from the catch drawer to a layer of cooler water below the surface of a waterbody generally at the trawl net operating depth.
In an alternative embodiment, a by-catch separating device is positioned downstream of the trawl net to provide means whereby escapement of by-catch species is naturally encouraged. The by-catch separating device is a short tubular section having an internal baffle or screen comprising a plurality of parallel, spaced apart members secured therein and biased against the incoming water flow. The internal baffle creates a downstream chamber wherein by-catch organisms unable to pass through the spaced apart members are directed toward one side of the separator which contains an escape aperture. A source of illumination is fixed externally of the separator in proximity to the escape aperture as an attractant to encourage by-catch to egress the downstream chamber through the escape aperture.
The members comprising the internal baffle or screen may be flexible, such as of nylon strings, and are generally parallel and spaced apart sufficiently so as to permit passage therethrough of all the target species. Where the lower size range of non-target species approximates target species size, a further separation is possible by placing a further by-catch separating device in series upstream of the primary. The internal baffle of the secondary separator, in order to separate out smaller by-catch, has the spaced apart members positioned closer together. Such separation will still permit a reduced quantity of smaller sized non-target organisms to be brought to the catch boat along with the intended target species.
Alternatively, a by-catch separating device may comprise a plurality of spaced apart internal baffle members wherein the nylon strings of successive downstream baffle members are positioned so as to permit passage of successively smaller sized non-target species.
Put another way, the device of the present invention for separating target and non-target species harvested from waterbodies includes in a broad sense a trawl net attached to a trawler by a line or cable or the like so as to be movable through the water when towed by the trawler, and a catch boat also attached to the trawl boat by another line or cable or the like so as to be movable concomitantly with the trawl net when towed by the trawler. However the trawl net and trawler per se do not form part of the invention as they are conventional with the exception that a hole is made in the cod end of the trawl net. In one embodiment, a catch drawer is mounted within the catch boat for selective vertical movement relative thereto by means for selective vertical movement of catch drawer. A conduit connects the leading end of the catch drawer to the cod-end of the trawl net so as to permit fluid communication in a flow of water from the cod-end through the conduit into the catch drawer of water from an operating depth containing both target and by-catch species.
A series of removable filters or screens are positioned in a spaced array within the catch drawer, spaced in a water flow direction from the front of the drawer to the back of the drawer. The screens or filters may have apertures cascading in a series of stepped sizes from, for example, larger apertures at the front filters to smaller apertures at the aft or rear filters. The screens or filters may be perpendicular to the flow direction, i.e., perpendicular to the longitudinal axis of the hull of the catch boat.
Where such by-catch has been reduced through introduction of a separating device, the catch boat may be a compartmentalized craft having a receiving compartment, a by-catch holding compartment and a discharge compartment. The receiving compartment contains by-catch diverting screens, a target species harvesting device and a pump. The pump is screened within the receiving compartment to prevent inadvertent loss of harvestable target species. The receiving compartment and discharge compartment are in fluid communication with each other through the holding compartment by way of manually controlled flow gates. The discharge compartment is in direct fluid communication with the water body to permit the reintroduction of entrapped by-catch to the water body.
Target species may be collected by suitable collection apparatus positioned within the catch boat or transferred directly to a nearby vessel, for storage or processing, through a suitable pump and conduit.
A pump may be provided within the catch drawer for pumping discharged fluid and by-catch along a second conduit leading from the pump to the operating depth to convey by-catch to the cooler water below the thermocline. Additionally, a selectively operable door in the aft end of the catch drawer may be provided to allow vacuum drawn discharge of by-catch to the water surface when seasonal thermoclines in the water are not prevalent.
In summary, the apparatus for separating target and non-target species harvested from a waterbody includes a catch boat towable behind a trawler for towing concomitantly with a trawl net towed behind the trawler. An elongate intake conduit having first and second ends extends between the catch boat and the rearmost (i.e. downstream end of the trawl net. The first end of the intake conduit is mountable to, so as to be in fluid communication with, an aperture in the trawl net, when the trawl net is submerged to at least a thermocline depth in the waterbody. The second end of the intake conduit is opposite the first end of the intake conduit and is mounted to the catch boat in fluid communication with a first fluid reservoir in the catch boat.
Fluid urging means are provided for urging fluid containing harvest species and by-catch along the intake conduit from the first end to the second end of the intake conduit so as to discharge fluid from the second end of the intake conduit into the first fluid reservoir. Outflow means are provided for discharging fluid and by-catch from the catch boat.
In one embodiment, the second end of the intake conduit is mounted in fluid communication with a first aperture in catch boat. The first aperture in the catch boat may be in a leading end of the catch boat, and may be below a waterline of the catch boat when floating in the waterbody.
The fluid urging means may also be a selectively vertically displaceable catch drawer mounted within a well in the catch boat. In this embodiment, the second end of the intake conduit is mounted to an intake aperture in the catch drawer, positioned so as to be submergible below a waterline of the catch boat when the catch boat is floating in the waterbody. The catch drawer is lowered relative to the well. The first fluid reservoir is contained within the catch drawer.
In the latter embodiment, at least one filter is mounted in the catch drawer and the outflow means is mounted within the catch drawer oppositely disposed from the intake aperture relative to the filter or filters. The filters may be an array of filters spaced apart between the intake aperture and the outflow means. Advantageously, the array of filters have screening sizes which decrease from a first end of the array adjacent the intake aperture progressively to an opposite second end of the array.
The outflow means may include a fluid pump communicating with an elongate outflow conduit which may be extended to a thermocline depth in the waterbody. The outflow means may further include a selectively operable gate in an aft end of the catch drawer.
The fluid urging means may be at least one water level regulating pump mounted to the catch boat in fluid communication with the first fluid reservoir. Fluid is pumped from the first fluid reservoir into the waterbody to thereby maintain a water level of the first fluid reservoir below a waterline of the catch boat when floating in the waterbody.
In the former embodiment, at least one by-catch screen directs by-catch to a second fluid reservoir in the catch boat. The outflow means may include an outflow conduit mounted in fluid communication with an outflow aperture in the catch boat and the second fluid reservoir. Advantageously, harvesting means such as an endless conveyor are mounted to the catch boat for harvesting harvest species from the first fluid reservoir.
In one preferred embodiment, not intended to be limiting, the intake conduit includes a screening tube for screening out by-catch. The screening tube has an aperture in a wall of the tube. A screen is mounted in the screening tube and positioned across a conduit passageway of the screening tube, adjacent the aperture in the wall. The screen urges by-catch out of the screening tube through the aperture in the wall. Advantageously a light source is positioned outside of the aperture to assist by luring the by-catch towards the light.
The screen may be a parallel array of uniformly spaced apart elongate flexible members. The array of flexible members may be mounted in the screening tube by journalling opposite ends of each member of the array of flexible members through corresponding holes in opposite walls of the screening tube. Each member of the array of flexible members may be tensioned by a resilient tensioner acting on some or all of the members whether singly or grouped.
In one aspect of this part of the invention, the screen is mounted in the screening tube at an acute angle relative to the wall to thereby form a wedge-shaped upstream cavity in the screening tube between the screen and the wall. The aperture in the wall is adjacent a vertex of the wedge-shaped cavity.
The fluid urging means may, in a further embodiment, be a second conduit placed coaxially within the intake conduit. The second conduit is at its second end connected to a pump which urges fluid under pressure toward a sealed first end of the second conduit which is positioned near the downstream end of the trawl net. Nozzles located along the second conduit direct pressurised fluid in a direction consistent with a flow toward the catch boat resulting in a lower pressure in the vicinity of the intake conduit.
The fluid urging means may, in a further embodiment, be a solid, annular flared collar secured to the first end of the intake conduit in proximity to the downstream end of the trawl net. As the apparatus is drawn through the water body the flared collar funnels liquid through the intake conduit toward the catch boat to thereby assist in the transportation of target organisms through the intake conduit toward the catch boat.
The fluid urging means may, in a further embodiment, be a hydraulic screw positioned within the intake conduit, in proximity to the catch boat, and rotatable by means well known in the art mounted on the catch boat.
The fluid urging means may, in a further embodiment, be a water wheel positioned within the catch drawer in proximity to the outflow aperture. Rotation of the water wheel by a motor and pulley arrangement located on the catch boat, or by other means well known in the art, acts to enhance liquid flow through the catch drawer from the intake conduit to the outflow aperture and into the waterbody. As the water wheel rotates at relatively low revolutions per minute it is ideal for assisting with the clearing of zooplankton and the like which may also be inadvertently brought to the surface.
Thus the method of the present invention includes the steps of:
(a) mounting an elongate intake conduit between the trawl net and the catch boat so that the first end of the intake conduit is mounted to, so as to be in fluid communication with, the aperture in the trawl net when the trawl net is submerged to at least a thermocline depth in the waterbody, and so that the second end of the intake conduit is mounted to the catch boat in fluid communication with a first fluid reservoir in the catch boat,
(b) towing a catch boat behind the trawler and concomitantly towing the trawl net behind the trawler,
(c) urging, by the fluid urging means, fluid containing harvest species and by-catch along the intake conduit from the first end to the second end of the intake conduit so as to discharge fluid from the second end of the intake conduit into the first fluid reservoir,
(d) discharging, by outflow means, outflow fluid and by-catch from the catch boat.